The use of cellular telephones and wireless networks has become increasingly widespread. As the use of cellular telephones has increased, the number and quality of additional features made available with the cellular telephones has also increased. For example, many cellular telephones now provide a “walkie-talkie” type of feature in which users may communicate with a selected person or group of people by pushing a button on the telephone. This feature is often referred to as “Push-To-Talk.”
The Push-To-Talk (PTT) feature is useful for situations in which users want or need to communicate with the same person or group of people repeatedly but not continuously. For example, a group of people at a mall may desire to keep in touch with each other after they split up to shop separately. Using Push-To-Talk, one person may quickly contact another person or other people without having to make a conventional cellular phone call.
The parties involved must first establish a PTT service between their respective phones. The wireless network is then aware of the presence of each mobile station (e.g., cell phone) involved in the PTT service, although no traffic channels are set up. The mobile stations initially communicate with the base stations of the wireless network using only overhead control channels to establish the PTT service. Once the PTT service is established, the call originator does not have to dial the number of the called party in order to communicate. The call originator only needs to press a button, wait for a beep (or a similar indicator), and then speak. Advantageously, many service providers do not charge these conversations against the users' allotted usage minutes for the cellular telephones.
Many conventional PTT services use Internet Protocol (IP) transport to provide PTT service. IP packets are transported between the wireless network and the originating and terminating mobile stations over a Radio Link Protocol (RLP) link (i.e., network layer) after traffic channels are set up. Immediately after the call originator pushes the button to initiate a PTT call, the wireless network verifies that the call terminating (or target) mobile station is still present on the network. If the target mobile station is still present, the wireless network sets up the physical layer of a traffic channel between the originating mobile station and the network base station. The physical layer of a traffic channel between the wireless network and the target mobile station is also set up at the same time. The physical layers of the traffic channels enable the originating and target mobile stations to receive and send data frames.
Next, the wireless network establishes a Radio Link Protocol (RLP) link layer between the originating and target mobile stations. The RLP link transports the IP packets on top of the data frames of the physical layers of the traffic channels. Finally, the wireless network sends to the originating mobile station a Flow Grant message. The Flow Grant messages is sent in IP packets over the RLP link. When the originating mobile station receives the Flow Grant message, it emits the beep or other indicator that informs the user (i.e., call originator) that the user may begin speaking.
However, there may be some significant latency (i.e., delay period) between the time when the user pushes the button to start using the PTT service and the time when the user receives a beep that indicates the user may speak. This latency is related to the initial delay in setting up the physical layer of the traffic channel between the wireless network and the originating mobile station and the further delay of setting up the network layer (i.e., the RLP link) between the originating mobile station and the wireless network. As a result, conventional cellular telephones may have delays of more than one second between the time that the user pushes the button and the time that the beep is provided. Such a delay can become annoying to the user and detracts from the PTT service.
Therefore, there is a need in the art for an improved Push-to-Talk service having a reduced latency. In particular, there is a need for an improved wireless network and mobile stations that reduce the latency in originating a Push-to-Talk or other type of delayed service session.